This invention relates to a voice recognition system and, more particularly, to a voice recognition system having a function of confirming the identity of the speaker.
Speaker confirmation systems in which a human voice spoken is analyzed to determine whether it is of a registered person may be applied to person certifying means in banks or check-in and check-out control systems, and their practical realization has been expected. Speaker confirmation systems are sometimes called speaker recognition or speaker check systems, and have long been studied.
A conventionally developed speaker confirmation system is based on a pattern matching method.
In this system, a voice pattern of a password of a registered speaker is stored in advance as a standard pattern A and at the time of confirmation, an input password voice pattern X spoken by the speaker is compared with the standard pattern to calculate the dissimilarity D (X, A). If the dissimilarity is less than a predetermined threshold value .theta., it is recognized that the input voice pattern coincides with the standard pattern. In this case, the speaker is determined to be the registered person. Conversely, if the dissimilarity is greater than the threshold value .theta., it is recognized that the two patterns do not coincide, and the speaker is determined to be an impostor.
The reliability of the prior art voice recognition system having a function of confirming the speaker as described above is greatly influenced by the magnitude of the threshold value .theta.. Erroneous operation of speaker confirmations systems are of two different kinds, i.e., a false rejection of the true registered speaker as an impostor and a false acceptance of an impostor as the true registered speaker. When the threshold value.theta. is reduced, the possibility of false rejection can be reduced, but the possibility of false acceptance is increased. Conversely, if the threshold value .theta. is increased, the false rejection can be reduced, but the false acceptance is increased.
In applications to the person confirmation in banks or check-in and check-out control systems, it is thought that the threshold value.theta. should be set to be rather low in view of the seriousness of the result that might occur from the false acceptance. This necessarily leads to a system that in case of a false rejection the speaker must pronounce the password repeatedly until it is properly accepted. This method, however, leads to a reduction in service in the case of person confirmation in banks or to a great inconvenience in check-in and check-out control systems.